1. Field of the Invention
This invention relates to an organic-based film, such as a resist film, formed on a layered unit having an organic-based low dielectric constant film exhibiting high reactivity to an oxygen plasma.
2. Related Art
An ultra-LSI device is demanded for integrating millions or more of devices on a chip each side of which measures only several mm. Since it is difficult to manufacture such highly integrated ultra LSI devices by simply miniaturizing the planar devices, a multi-layer interconnection structure of stacking the devices in plural layers is used. This multi-layer interconnection structure is indispensable in manufacturing a highly integrated ultra LSI.
The ultra LSI is also demanded for a high device function and a higher operating speed, and hence the prompt development of semiconductor forming process technique satisfying this demand is mandatory. The above-mentioned multi-layer interconnection technique may be mentioned as one of the types of the semiconductor forming process techniques.
However, with a device having the multi-layer interconnection structure, the inter-layer capacitance in the multi-layer interconnection structure is increased, as a result of which the signal delay time is also increased. Therefore, in keeping with the above-mentioned multi-layer interconnection technique, it is necessary to decrease the interlayer capacitance for shortening the signal delay time.
For meeting this demand, attention is directed to the low dielectric constant insulating film, as an inter-layer insulating film, and various investigations are being conducted on it. This low dielectric constant insulating film is classified into a film formed of an inorganic based film and an organic based film.
As the inorganic based films, a SiOF film is used in view of ease in film forming by plasma CVD. However, this SiOF film, low in dielectric constant among inorganic based materials, has a dielectric constant ∈ of the order of 3.5, such that it cannot sufficiently reduce the above-mentioned interlayer capacitance. Therefore, the inorganic-based low dielectric constant insulating film is thought to be insufficient for use as an inter-layer film in the ultra-LSI device.
On the other hand, there are many organic materials having a lower dielectric constant of 2 to 2.5 so that the above-mentioned inter-layer capacitance can be reduced sufficiently. Therefore, the low dielectric constant insulating film employing the organic materials is thought to be promising as the ultra-LSI.
Meanwhile, the low dielectric constant insulating film formed of the organic material is used in such a configuration that SiO2 layers as protective layers are formed as upper and lower layers. These protective layers reduce the effect of the organic low dielectric constant insulating film on the interconnection layer.
In forming the organic low dielectric constant insulating film, usually the SiO2 films of the upper and lower layers are formed by CVD and the organic low dielectric constant insulating film is formed by rotating coating.
The organic low dielectric constant insulating film is processed for forming connection holes or grooves reaching the interconnection layer. For this processing, techniques such as usual photolithographic techniques are used, and a resist mask formed of an organic material is formed on top of the organic low dielectric constant insulating film. Then, after desired processing, the resist mask is stripped. This stripping of the resist mask is usually by ashing by oxygen plasma. That is, with the conventional technique, the resist mask is stripped from the organic low dielectric constant insulating film by ashing with an oxygen plasma.
This ashing method is a technique for completely stripping the resist mask formed of an organic material. However, since the organic low dielectric constant insulating film is formed of an organic material similar to the resist mask material, it is a frequent occurrence that the organic low dielectric constant insulating film is ashed together with the resist mask.
The organic low dielectric constant insulating film then ceases to function as the inter-layer film having desired characteristics. That is, this technique experiences a problem that a device having an organic low dielectric constant insulating film cannot be processed to a desired shape.
It is an object of the present invention to provide a method for stripping an organic film which is applied for processing the organic low dielectric constant insulating film to a desired shape and which can easily strip the organic film formed on top of the organic low dielectric constant insulating film.
In one aspect, the present invention provides a method for stripping an organic film formed on a layered unit having at least an organic low dielectric constant insulating film including generating radicals in a gas mainly composed of fluorine-based gas and stripping the organic film by said radicals.
With the present method for stripping the organic film according to the present invention, the organic film is stripped by radicals generated in the gas mainly composed of a fluorine-based gas. These radicals are lower in reactivity with the organic low dielectric constant insulating film than with the organic film and hence are not reacted with the organic low dielectric constant insulating film. Thus, with the present technique, the organic film can be stripped from the organic low dielectric constant insulating film without the risk of ashing thereof.
In stripping the organic film according to the present invention, it is also possible to add oxygen to the gas mainly composed of the fluorine-based gas.
By adding oxygen, the radical generating reaction for the fluorine-based gas is accelerated to permit radicals to react efficiently with the organic film.
In another aspect, the present invention provides a method for stripping an organic film formed on a layered unit having at least an organic low dielectric constant insulating film including generating radicals in a gas mainly composed of ammonia and stripping the organic film by these radicals.
In the method for stripping the organic film according to the present invention, an inert gas can also be added to the above-mentioned gas composed mainly of ammonia.
In this case, by adding the inert gas, it is possible to control ammonia to desired concentration and hence to control the amount of yielded radicals. Thus, with this technique, the organic film can be stripped with a controlled stripping rate.
In yet another aspect, the present invention provides a method for stripping an organic film formed on a layered unit having at least an organic low dielectric constant insulating film, including stripping part of the organic film formed on a layered unit at least having an organic low dielectric constant insulating film, and subsequently stripping the remaining portion of the organic film by radicals generated in a gas mainly composed of ammonia.
In this stripping method for the organic film according to the present invention, part of the organic film is first stripped by radicals generated in the gas mainly composed of the fluorine gas, and the remaining portion of the organic film is stripped by radicals generated in the gas mainly composed of ammonia. That is, with the technique, the organic low dielectric constant insulating film is ashed in two separate steps. First, the organic film is ashed by radicals generated in the gas mainly composed of the fluorine-based gas. Subsequently, the remaining portion of the organic film is completely stripped by radicals generated in the gas mainly composed of ammonia. This technique permits complete stripping of the organic film formed on the layered unit.
With the method for stripping the organic film according to the present invention, the organic film can be positively removed without the risk of stripping the organic low dielectric constant insulating film, because of the low reactivity between radicals removing the organic film and the organic low dielectric constant insulating film. Thus, with this technique, a semiconductor device having a desired shape can be manufactured without incurring the risk of etching the organic low dielectric constant insulating film.